1. Field of the Invention
The present invention relates to a fuel supply apparatus for an internal combustion engine, especially to an improved structure of the fuel supply apparatus to maintain supplied fuel pressure at a set value by detecting the fuel pressure supplied to a delivery pipe with a pressure sensor and by adjusting a fuel discharge amount of a fuel pump.
2. Description of Related Art
FIG. 10 shows a conventional fuel supply apparatus for an internal combustion engine with a delivery pipe. A fuel supply pipe 22 extending from a fuel pump 1 disposed in a fuel tank 7 is connected to a delivery pipe 2 through a filter 23. Plural fuel injection valves (injectors) 21 disposed corresponding to each cylinder of an engine (not shown) are. connected to the side wall of delivery pipe 2.
A discharge amount of the fuel (rotational speed) of fuel pump 1 in this case is fixed. When a supplied fuel amount of injectors 21 changes according to a running condition of a vehicle, the internal pressure in delivery pipe 2 varies. Since the change of the fuel pressure in delivery pipe 2 causes fluctuation of an injection amount of injectors 21, a pressure regulating valve 24 is disposed in delivery pipe 2 as shown in the figure to maintain the fuel pressure in delivery pipe 2 at a constant value.
When pressure regulating valve 24 is disposed, however, a return pipe 25 for returning the fuel to fuel tank 7 is also needed, thus requiring a piping space in the engine compartment and a work for connecting the pipe. Furthermore, since pressure regulating valve 24 is disposed in delivery pipe 2, the fuel receiving heat from the engine returns to fuel tank 7, and a large amount of evaporated fuel is generated in fuel tank 7.
In light of the above-described problems, in a fuel supply apparatus as disclosed in JP-A-6-50230, a manifold with a built-in pressure sensor is disposed at the outlet of the fuel supply pipe in the fuel tank to maintain the fuel pressure, detected by the pressure sensor and supplied to the delivery pipe, at a constant value by controlling the rotational speed of the fuel pump. In this structure, the aforementioned pressure regulating valve for maintaining the internal pressure of the delivery pipe at the constant value and a piping for the valve are not needed.
In the fuel supply apparatus disclosed in the above-described publication, however, since the pressure regulating valve of the delivery pipe is eliminated, the delivery pipe is closed when fuel injection stops, e.g., the internal combustion engine is stops or fuel is cut off. Thus, the fuel in the delivery pipe receives residual heat of the engine to thereby raise the temperature. Accordingly, when the fuel is expanded in its volume or vaporized in the delivery pipe, there causes a problem that the internal pressure becomes abnormally high.
To solve this problem, a relief valve may be disposed at the downstream side of the check valve in the manifold to restrain the internal pressure of the delivery pipe from rising. In this case, the structure of the manifold with the built-in pressure sensor becomes so complicated that it is more difficult to manufacture the manifold.